With the progress of a large variety of technologies, many electronic components have developed gradually along the microminiaturization and the diversification, and a design of a printed circuit board assembly (PCBA) with the electronic components thereon is more complex. Therefore, it is important to decide what way to protect the PCBA from being moistened by some exterior chemicals, the quality of protection usually determines the operating life of the PCBA. In order to solve the problem that the PCBA could be moistened, it usually forms a protective film on the PCBA in prior arts. In addition, some other devices may need a protective film for keeping from being moistened and less friction, such as, some cables.
However, a prior art technology usually uses a coating process to protect the PCBA and the other devices, but the traditional coating process is easy to make a thickness of the protective film too thick or with non-uniform distribution. Another prior art technology employs a vapor deposition process to form the protective film on the PCBA, but the vapor deposition process often makes the protective film not be uniform because of placed angles of the electronic components. Therefore, a method forming a thinner protective film with high quality protection function and more uniform distribution is required.